Pulley Ridge is a series of drowned barrier islands that extends almost 200 km in 60-100 m water depths. This drowned ridge is located on the Florida Platform in the southeastern Gulf of Mexico about 250 km west of Cape Sable, Florida. This barrier island chain formed during the initial stage of the Holocene marine transgression. These islands were then submerged and left abandoned near the outer edge of the Florida Platform. The southern portion of Pulley Ridge hosts zooxanthellate scleractinian corals, green, red and brown macro algae, and a mix of deep and typically shallow-water tropical fishes. This reef community is in unusually deep water, and its extent and the controls on its distribution were unknown. To address these questions scientists from the U.S. Geological Survey Coastal and Marine Geology Program in cooperation with scientists from the University of South Florida Department of Marine Sciences have completed a detailed mapping of the southernmost 35 km of Pulley Ridge. The area was mapped using multibeam bathymetry, sidescan-sonar imagery, and high-resolution seismic-reflection profiling to define the geologic framework on which the reef is established. Submersible dives, remotely operated vehicle (ROV) transects, and transects of bottom photographs and video were collected to identify the corals and to map their distribution. This extensive suite of data has been compiled and preliminary analysis of the data suggests that the reefs are not tied to the ridge system, but instead are more broadly distributed. Whether reef distribution is controlled by oceanographic conditions or by subtle differences in the substrate that overlies the barrier island system is unclear, and are topics of continued research.

Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 1.000000
Ordinates (y-coordinates) are specified to the nearest 1.000000
Planar coordinates are specified in meters

The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257224.

The digital sidescan data were then processed and mapped to provide proper geographic locations of features identified in the imagery. The processing steps included subsampling the raw sidescan data using a median filtering routine to suppress speckle noise and reduce file size, and correct for slant-range distortion, signal attenuation, and dropped sonar lines using XSonar (Danforth et al., 1991). After these processing steps, the imagery was mapped into its proper geographic location using techniques summarized by Paskevich (1996). Individual sidescan swaths were mapped with each pixel geographically positioned at a resolution of 1 m/pixel.

A linear stretch was applied in PCI to the sidescan image. This stretch was from 0-255 with resulting values between 0 and 254. This was done so that the white background (255) could be made transparent in the GIS.

The ship was navigated with Differential GPS which has an assumed accuracy of better than 10 meters. A transponder was used to range to fish, which introduces additional positional accuracy of the sidescan imagery.

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